A device for recovery of static energy from working engines is disclosed in PCT/WO 93/11363. Two hydraulically operable working cylinders execute the raising and lowering of the working tool, and are connected in fluid communication at the rod end one below the other. In this known device, the piston chamber of the hydraulically operable working cylinder is connected with the hydraulic accumulator through a cartridge-valve cooperating with a distributor of control energy, which distributor is connected to a pressure relay as part of a control arrangement. This control arrangement is connected by its control input to a low pressure branch of the hydraulic circuit, which cooperates with the movable parts of the working engine in the form of the working tools. Using this known device, upon lowering the working tool, the quantity of fluid on the piston side of the working cylinder can be discharged with inclusion of the static energy under pressure which is being dissipated at the hydraulic accumulator. From the hydraulic accumulator, the energy can be drawn back again exactly quantifiably for the subsequent raising of the working tool. By this means, greater amounts of energy can be recovered than with the devices known until this time.
Despite the good energy recovery behavior of this known device, it has certain drawbacks. In this device, while holding the working tool, following a lowering procedure, the cartridge-valve is inclined to "flutter". Therefore, the working tool, usually in the form of an extended arm, begins to luff. This undesired movement of the working tool can be lessened only with inclusion of a very costly control device mounted on its periphery. With lowering of the working tool under a load, the cartridge-valve opens in sudden, erratic bursts. When the hydraulic accumulator is emptied and there is a high load thrust. A slow lowering for a small stretch, for example for a few millimeters, cannot be executed. There is also lessened capacity for working. Thus, additional force is required to accomplish the lowering procedure, since the hydraulic accumulator with increasing fluid filling works counter to this force and reduces the effect of the force during lowering procedure.
In another known device for recovery of energy, disclosed in EP 0 230 529 B1, an identical cartridge-valve is used especially for recovery of hydrostatic braking energy in motor-powered vehicles, such as trucks or buses. In addition to the cartridge-valve, the valve arrangement of this known device for energy recovery also requires a multi-way valve and three impedances arranged at various points in the circuit, which in all heightens the susceptibility to interference of this known device.